The present application relates to a process for the preparation of wholly aromatic polyamides.
Wholly aromatic polyamides, being among the most important of the synthetic polymers, are prepared by a variety of methods including melt polymerization, solution polymerization, solid state polymerization and the like. Generally, these processes are carried out without substantial concern relating to the mode and rate of introduction of monomers to the reaction vessel employed since the polymerization reaction is such that low molecular product is maintained in a state where it can undergo further reaction to form the desired higher molecular weight product. In the solution polymerization of aromatic diamines and aromatic diacid halides, however, the rate of reaction approaches or exceeds the rate of mixing of the monomers. Additionally, in the reaction of certain of these diamines and diacid halides, the viscosity of the reaction mix increases rapidly and a non-flowing gel is formed. Thus, in the solution polymerization, if dissolution and complete mixing of the diamines and diacid halides does not take place within a very short period of time, proper stoichiometry is not achieved and the resulting polyamide product has a lower than desired molecular weight.
Another problem encountered in the solution polymerization employing the diacid halide monomer is the interaction of the diacid halide with the solvent. In many instances, the solvent that gives the optimum polymer molecular weight is reactive toward the diacid halide and solutions of satisfactory purity and reactivity can not be prepared or held for a reasonable length of time.
Typically, the solution polymerization of aromatic diamines and aromatic dicarboxylic acid halides is carried out by bringing together separate solutions of these two monomers or by combining a solution of one of the monomers with the solid, pure, form of the other monomer. The combining of separate solutions of the monomers does not give satisfactory results, particularly on a large scale, because suitable mixing of the reactants before the reaction mixture becomes highly viscous or gel-like may not be possible because of the rapid rate of polymerization. Frequently, the reaction between the acid halide and polymerization solvent mentioned above excludes this two solution technique. The combining of a solution of one type of monomer with the solid form of the second type of monomer is not feasible on a continuous basis because the continuous feeding of the reactants to a reactor in a manner so as to maintain a stoichiometrically balanced system producing high molecular weight polymer is technically difficult. Methods of reacting aromatic diamines and aromatic diacid halides typical of the methods employed heretofore are described in U.S. Pat No. 3,063,966 to Kwolek et al.
It is an object of the present invention, therefore, to provide an improved process for preparing wholly aromatic polyamides that will avoid problems associated with the prior art processes.
It is another object of the present invention to provide an improved solution polymerization process for preparing wholly aromatic polyamides from solid particulate monomers, namely, aromatic diamines and aromatic diacid halides. These and other objects, as well as the scope, nature and utilization of the invention will be apparent to those skilled in the art from the following description and the appended claims.